What settings will allow better CPU performance?

So typically, stuff like texture, shadows and anti-aliasing allow the GPU to have more breathing room to increase its frame rate. But how about the CPU? What settings when adjusted will change the CPU's load?
My years old CPU is basically the bottleneck that's stopping me from spawning more traffic cars, so I'm looking to see if there's anything I could do to free up CPU load.

 

maybe turn on simplified physics, turn on the fps limiter if possible ?

 

Get a new cpu? The game is really cpu dependent so there's not much you can do except the aforementioned simplified physics. I would also consider overclocking if possible, which could improve single core performance, although I don't think it would have much of an effect on how many cars you could spawn in traffic mode.